Fluid sampling is used to acquire a manageable representative collection volume of a much larger volume. Automatic liquid sampling is used when accurate samples at steady intervals are required to accurately acquire a reliable representation of the bulk volume. The sampled liquids are send to a location, most of the time a laboratory, where the volume can be analyzed and its content can be determined.
Liquid sampling devices are used over 50 years and perform a major role in the qualitative measurement, in particular in oil and gas industry. These sampling devices may for instance be mechanical operating constant volume pumps. The sampling device usually comprises a sample extraction channel in fluid communication with a main flow through a main pipeline, for example an oil pipeline. A sample can be separated from the main flow by pressing a sample in the sample extraction channel. The sample extraction channel may be provided with one or more check valves to avoid that the sample flows back into the fluid flow or that fluid undesirably enters the sample extraction channel.
A prior art sampling device is disclosed in GB2116521. This prior art sampling device comprises a pressure balanced check valve.
The check valves, in particular the sealing surfaces of the check valves are subject to wear. Especially when the liquid is not a clean pure substance but contains hard solids, like sand or has a high viscosity or pressure, the performance of the sampling device deteriorates over time. The wear of the sampling device and deterioration of its performance is mostly due to seal leakage causing sampled liquids to leak to the main fluid flow or to the environment or main flow liquid leaking into the sample volume area.